An introduction to pulse width modulation speed control
Pulse Width Modulation (PWM) is how we control motor speeds from a digital control system. Instead of varying the voltage supplied to a motor, we use pulses to control it. The pulses are usually at a fixed rate, but the ratio of time-on to time-off changes. We call this the duty cycle. Controlling how much time per cycle the signal is on versus off will control the power getting to a motor. If the pulse is on for longer, the motor will go faster. The motor will go slower if the pulse is on for less time. So, at 50% time-on, the motor will be about 50% of its maximum speed.
The following diagram shows visual examples of this:
Figure 5.6 – PWM signals
The preceding diagram shows graphs of PWM signals. The top is a signal for driving a motor at half speed. The pulses on and off time are the same. The X axis is the level, and the Y axis is for time, with a solid line for the PWM signal and a dashed...
